Abstract
A phospholipid vesicle encapsulating a concentrated hemoglobin solution and pyridoxal 5'-phosphate as an allosteric effector (Hb-vesicle: diameter, 250 nm) has been developed as an oxygen carrier. The oxygen release from flowing Hb-vesicle was examined using an oxygen-permeable fluorinated ethylenepropylene copolymer tube (inner diameter, 0.028 mm) under deoxygenated environment. The oxygen release was measured using a scanning-grating spectrophotometer constructed on an inverted microscope. The rate of oxygen release was determined based on the visible absorption spectrum. Hb-vesicles and fresh human RBCs were mixed in various ratios at [Hb] = 100 g/L in isotonic saline containing 50 g/L albumin, and the suspension was perfused at the centerline flow velocity of 1 mm/s through the narrow tube. The Hb-vesicles were homogeneously dispersed in the isotonic saline. With increasing the amount of the Hb-vesicles resulted in a thicker marginal RBC-free layer. Irrespective of the mixing ratio, the rate of oxygen release from the Hb-vesicle-RBC mixtures was similar with that from RBC alone. However, the addition of 50 vol% Hb solution to RBCs enhanced the release of oxygen. In conclusion, the difference in the rate of oxygen release between Hb-vesicles and Hb should mainly be due to the difference in the particle size (250 vs. 8 nm), namely in the oxygen diffusion distance. [Jpn J Physiol 54 Suppl:S114 (2004)]
